This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The addition of carbohydrates is a frequent posttranslational modification of proteins. In fact, it is estimated that half of all mammalian proteins are glycosylated. Yet we have few means of structurally characterizing these proteins in their native glycosylated state. NMR methods provide a potential source of structural models, but a prerequisite is assignment of resonances to specific sites within the protein. The requirement for expression of proteins in cells that can glycosylate often prohibits use of common methods for assignment that rely on uniform labeling with 13C, 15N, and 2H. We are developing an alternate strategy that works with just sparse 15N labeling of select amino acids. It links NMR resonances with mass spectrometry (MS) fragment identification through amide proton exchange rates that can be measured by both NMR and MS. This work began with applications to a simple model protein, Galectin-3, but is now shifting to the glycosylated gycosyltransferases, ST6Gal-I and FucT-III.